1. Field of the Invention
The present invention relates to an optical system, an image scanning exposure apparatus, and a method for arranging point light sources in the optical system, wherein the optical system is formed by a light source portion comprising a plurality of point light sources mounted on a substrate, and by a single imaging lens system which allows light from the light source portion to form an image, and wherein the image scanning exposure apparatus includes a light source portion with a plurality of point light sources mounted on a substrate, a single imaging lens system which allows light from the light source portion to form an image on a photosensitive material, a main scan driving system which moves a unit integrally structured by the light source portion and the imaging lens system in a predetermined main scanning direction, and a sub-scan driving system which moves the photosensitive material stepwise in a direction perpendicular to the main scanning direction for each main scanning operation.
2. Description of the Related Art
Currently, a number of image exposure apparatuses each having a digital exposure system mounted thereon have been developed. Generally, in the digital exposure system, an image is recorded on a recording medium in such a manner that a light beam outputted from a semiconductor laser is modulated with image data and deflected by the high-speed rotation of a polygon mirror (main scanning), and the light beam reflected by the polygon mirror is further subjected to sub-scanning by a galvano mirror or the like, or the above main scanning is effected repeatedly while the recording medium is moved (or the recording medium is moved stepwise). Here, as the recording medium, a photosensitive drum electrified by corona discharge, or a photosensitive material may be used. Further, in place of the semiconductor laser, another light emitter such as a light emitting diode (LED) may be used as a light source.
Here, there exists a main scanning system in which a plurality of light sources are arranged in a matrix form longitudinally and crosswise and a main scanning operation of a plurality of lines can be effected by one main scanning movement.
In this case, when a structure having a single lens system is used to form an image on a recording medium, pincushion distortion (see FIG. 7C) or barrel distortion (see FIG. 7D) is caused on an imaging surface due to distortion aberration. The size or form of the distortion varies depending on the optical system being used (degree of lens aberration, length of an optical path, focal length, and the like) and is set by determining setting conditions such as the arrangement of the optical system.
Non-uniformity of intervals among main scanning lines arises due to the distortion aberration, thereby resulting in deterioration of image quality.